Systems help...please?
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Posts: 46,084
I've found myself in the process of developing a test system for a black box
of sorts (I know what it is, but I can't tell you. NDAs and all) with a
rather short deadline. As I'm relatively familiar with the stamp, I figured
I could use it as the basis for my test system. It should also make the
rapid development time a little easier to cope with.
First off, I need to be able to spit a 16 bit number out of the stamp II
with shiftout. From a recent conversation with the boys at Parallax tech
support, it seems that contrary to what is implied in the v1.9 manual, the
limit for the data length in shiftout is a single byte. I need a word. I
think I can do this with a pair of sequential shiftout instructions using
the highbyte.word and lowbyte.word for the data argument. I'm going to be
sending this data out of a pair of shift registers cascaded together. I'm
planning on using the 74F164.
Thought and opinions?
Now for the kicker. I need to interface a few lines from the black box to
the stamp. The black box runs on 3.3V. I can get the output voltage
translated with a few voltage divider resistors on some of the pins, but I
will need some kind of bidirectional level shifter for the 8 pins that form
a data bus of sorts.
Is there a bidirectional level shifter for allowing 3.3V parts to speak to
5V ones?
And as is common in the R&D world, I need to finish this project last
Tuesday. Any information you guys can give me would be helpful.
-dave
Dave Paton Motorola Advanced Technology Center
voice 847.538.7575 pager 888.773.6802
A13593@e...
of sorts (I know what it is, but I can't tell you. NDAs and all) with a
rather short deadline. As I'm relatively familiar with the stamp, I figured
I could use it as the basis for my test system. It should also make the
rapid development time a little easier to cope with.
First off, I need to be able to spit a 16 bit number out of the stamp II
with shiftout. From a recent conversation with the boys at Parallax tech
support, it seems that contrary to what is implied in the v1.9 manual, the
limit for the data length in shiftout is a single byte. I need a word. I
think I can do this with a pair of sequential shiftout instructions using
the highbyte.word and lowbyte.word for the data argument. I'm going to be
sending this data out of a pair of shift registers cascaded together. I'm
planning on using the 74F164.
Thought and opinions?
Now for the kicker. I need to interface a few lines from the black box to
the stamp. The black box runs on 3.3V. I can get the output voltage
translated with a few voltage divider resistors on some of the pins, but I
will need some kind of bidirectional level shifter for the 8 pins that form
a data bus of sorts.
Is there a bidirectional level shifter for allowing 3.3V parts to speak to
5V ones?
And as is common in the R&D world, I need to finish this project last
Tuesday. Any information you guys can give me would be helpful.
-dave
Dave Paton Motorola Advanced Technology Center
voice 847.538.7575 pager 888.773.6802
A13593@e...
Comments
>with shiftout. From a recent conversation with the boys at Parallax tech
>support, it seems that contrary to what is implied in the v1.9 manual, the
>limit for the data length in shiftout is a single byte. I need a word.
Shiftout does words:
shiftout dpin,cpin,mode,[noparse][[/noparse]data\16]
The \16 specifies 16 bits. You can use \1 to \16 in that position.
Default is 8.
>I need to interface a few lines from the black box to
>the stamp. The black box runs on 3.3V. I can get the output voltage
>translated with a few voltage divider resistors on some of the pins, but I
>will need some kind of bidirectional level shifter for the 8 pins that
form
>a data bus of sorts.
>Is there a bidirectional level shifter for allowing 3.3V parts to speak to
>5V ones?
The CD4050 can be used instead of resistors to translate from +5 input to
+3.3 output.
And,
http://www.pericom.com/specs/PI74LPT245.pdf
is an "octal 3.3 volt bidirectional transceiver with 5 volt tolerant i/o".
Digikey carries it.
BTW, the stamp input threshold is 1.3 volts, so you can safely drive the
stamp inputs high with 3.3 volts.
-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com